DISSERTATION RESEARCH: Empirical, theoretical, and comparative tests of major hypotheses for the recurrent evolution of self-fertilization

Washington State University, Pullman WA

Investigators

Abstract

The goal of this project is to evaluate the underlying mechanisms that drive the evolution of the ability for flowering plants to self-fertilize. This goal will be accomplished by measuring the rate at which lineages transition from outcrossing to self-fertilizing in the mustard family, a diverse and agriculturally important group. Flowering plants display an incredible breadth of variation in flower size, shape, and color that is generally attributed to the co-evolution of flowering plants and pollinators. Considering the potentially important role of cross-pollination in evolution, it is surprising that the shift to self-fertilization is one of the most common evolutionary transitions in flowering plants. Despite decades of work on this subject, it is still not clear what drives the initial spread of selfing and tests of the leading hypotheses explaining this pattern are rare. One reason for this is that a series of rapid changes in other floral traits occur in response to selfing, which then act to obscure traditional methods of comparative inference. Additionally, the project will result in the training of graduate and undergraduate students. In flowering plants, shifts from outcrossing to selfing and from diploidy to polyploidy are common and are thought to occur in concert An association between selfing and polyploidy can occur through three non-mutually exclusive pathways. First, polyploidization could act as a filter, limiting the founding of new populations to those that originate from a self-compatible progenitor. Second, polyploidization could provide strong reproductive assurance resulting in the joint transition of mating system and ploidy. Finally, polyploidization could create a favorable environment for the spread of selfing after the population is established. This research estimates the transition rates of these three pathways in the Brassicaceae by assembling a database of mating system and ploidy data and extending a multi-state comparative model. These estimates will be used to evaluate the relative importance of reproductive assurance in the spread of selfing in neopolyploids. The model will show why simultaneous transitions to selfing and polyploidy are relatively rare in Brassicaceae and other families with sporophytic self-incompatibility (SI). The theoretical framework will be extended to explain why such SI systems can survive extreme population bottlenecks associated with polyploidy and island colonization.